1. Field of the Invention
The present invention relates to a hard plating method for the purpose of giving abrasion resistance to the sliding surfaces of mechanical parts or the like.
2. DESCRIPTION OF THE PRIOR ART
As such abrasion-resistance hard plating, generally, hard chromium plating has been performed. Hard chromium plating however has a defect in that if it is exposed to a high temperature not lower than 400.degree. C., it is softened to lose its abrasion resistance. That is, although hard chromium plating has Micro Vickers hardness of Hv. 800-1000 at a room temperature, if it is exposed at a temperature of 600.degree. C. for an hour, its hardness becomes low to Hv. 400 or less so that it loses its abrasion resistance. In order to improve such a defect, recently, various hard plating methods have been developed.
For example, composite plating in which fine powder of silicon carbide is contained as co-deposition in electroless nickel-phosphorous alloy plating has been put into practical use. The hardness and abrasion resistance of the composite plating is however not sufficient. Nickel-tungsten alloy plating has been known as precipitation hardenable alloy plating which is hardened through heat treatment. That is, this nickel-tungsten alloy plating has hardness of Hv. 600, and if the nickel-tungsten alloy plating is heat-treated at 400.degree. C. for an hour, the hardness thereof becomes Hv. 1150 at maximum. The nickel-tungsten alloy plating however has a defect in that the internal stress thereof is so high that large cracks may occur in the plating layer if the plating is performed thickly, resulting in a problem in practical use.